Saving seats by leaving belongings on a table is a customary practice seen in various public settings like cafes, libraries, and university common areas. This method of reserving a spot by placing a coat, a bag, or other personal items on a chair or a table serves as a visual signal to others that the space has been temporarily claimed. However, the social norms and reactions associated with this practice can vary widely, depending on several factors including the location, the duration for which the items are left unattended, and cultural attitudes toward public space sharing.

### Historical and Cultural Context
The practice of saving seats with personal belongings does not have a singular origin, but it is deeply embedded in the etiquette of public space usage in many cultures. Historically, saving a seat in this manner is a non-verbal way of indicating that someone has temporarily stepped away but intends to return. This method can be traced back to various informal rules governing public conduct in communal spaces, particularly in Western societies where personal space and property are highly valued.

### Social Etiquette and Norms
In most Western cultures, the temporary reservation of public seating by leaving personal items is generally accepted if the person is only gone for a short period. This might be just long enough to order food at a cafe or retrieve a book in a library. The unspoken rule here is that shorter durations—typically a few minutes—are more socially acceptable.

However, if belongings are left unattended for an extended period, this can lead to frustration and inconvenience for others, especially in busy settings where seating is limited. In these instances, it's not uncommon for someone waiting for a seat to move the unattended items after a reasonable amount of time has passed or even ask staff members for intervention.

### Reactions and Interaction
How people react to unattended belongings can vary. Some might simply choose another spot, while others might see prolonged absence as an implication that the seat is, effectively, no longer reserved. In certain social settings, if seating is scarce, others may feel justified in moving belongings aside after a certain waiting period. There’s often an internal calculation of wait-time fairness, with most people feeling that anywhere beyond 15-20 minutes is too long for items to be left unsupervised.

When someone does decide to move another's belongings, they typically do so with caution and respect, reflecting a universal understanding of personal property. Conflict or confrontation is rare, as most adhere to non-confrontational approaches.

### Legal and Institutional Policies
Some establishments have specific policies regarding this practice. For example, libraries and universities might post rules about how long items can be left unattended before they are considered abandoned. In such cases, staff may remove belongings to a lost and found area after a certain period. These policies help manage the space and ensure fairness for all users.

### Conclusion
The act of leaving belongings on a table to save a seat while briefly away is a widely recognized practice, tolerated within the boundaries of quick errands. However, when such belongings are left for extended durations, it can prompt others to intervene by asking about the ownership of the items, moving them, or seeking help from authority figures in the vicinity. The social acceptability of this practice ultimately hinges on the context of the environment and cultural expectations regarding public conduct and sharing spaces.